Dry-stack masonry blocks have been known and used for many years. They are quite popular because they do not require extensive site preparation or the services of skilled craftsmen. Instead, dry-stack masonry blocks allow most any able-bodied person to create a variety of structures, typically low walls or planters. In such applications, the blocks usually have sufficient weight to resist forces exerted by retained material (for example, such as soil and gravel backfill). However, as the height of the structures becomes greater they are subjected to forces exerted by the material being retained, and one or more blocks may become dislodged and/or a portion of the structure may bulge or bow outwardly and/or forwardly. This creates not only aesthetically displeasing view, but also a potentially hazardous condition. That is, dislodged blocks detract from the overall pattern and design of the structure and dislodged blocks may fall and injure a passerby, or fall and subsequently obstruct the normal flow of traffic. Understandably, such conditions require timely repair in order to minimize adverse consequences. This usually entails removing some backfill, removing the dislodged blocks and resetting them in their proper orientation, and then replacing the backfill. Sometimes this must be done more than one time, particularly if drainage is a problem. In extreme cases, the entire structure may have to be deconstructed and rebuilt. As one may imagine, such repair work adds to the total cost of the structure.
Attempts to counteract the forces involved in structures such as retaining walls have taken several approaches. One approach that is quite common to the industry is to manufacture the masonry blocks so that when they are assembled into a retaining wall structure, the retaining wall has an upwardly receding slope or batter. This slope, or batter, is usually accomplished by interlocking adjacent courses of blocks. Typically, this may include integrally formed projections that extend upwardly or downwardly relative to the block and which serve to position a block in a predetermined relation to adjacent courses of blocks. Alternatively, this may include pins or pegs that are configured to fit into vertically oriented holes in the top and bottom surface of the blocks and which serve to tie blocks in adjacent courses to each other. This approach has proved to be quite effective in medium sized wall structures. However, as retaining wall structures grow higher and higher, even these approaches sometimes fail and blocks can become dislodged and/or walls may collapse.
In order to solve this shortcoming, many of the above-mentioned retaining wall constructions are provided with flexible, pliant anchor grids of sheet-like plastic material, commonly known in the trade as a geo-grid. In use, flexible anchor grids are installed as the retaining wall is constructed with one end of the flexible grid positioned between adjacent courses of blocks and the remaining portion of the flexible grid extending onto the material being retained, where it becomes embedded as succeeding courses are laid and more backfill material is added.
As one may expect, retention of a flexible anchor grid between courses of blocks in a wall structure is of utmost importance, and there have been several approaches to flexible anchor grid retention, each of which have met with varying degrees of success. One approach, common to blocks with integrally formed projections or indexing flanges is to merely position the flexible grid between adjacent courses of blocks during wall construction. This creates several right angle bends at the end of the flexible grid, which results in increased frictional resistance to movement between the blocks and the flexible grid (see, for example, U.S. Pat. No. 5,294,216). A drawback with this approach is that the frictional forces may be overcome and a block or blocks may become dislodged. Another drawback is that when a flexible anchor grid is bent over at a right angle, the longitudinal strands can lose strength and cause the flexible grid to fail prematurely. Moreover, the flange, against which the flexible grid is positioned, may dig into and sever the longitudinal strands of the flexible grid and also cause premature failure.
Another approach, common to those blocks that utilize pins or pegs to connect adjacent courses of blocks is to connect the flexible grid to the pins by looping them about the pegs (see, for example, U.S. Pat. No. 4,914,876). A drawback with this manner of connecting the flexible grid to the blocks is that forces are concentrated at points rather than along the width of the flexible grid. That is, the connecting pins contact the transverse strands of the flexible grid at only two points. As one may imagine, this can lead to premature failure and possible dislodgement of the blocks. Moreover, some flexible grids are manufactured so that the longitudinal strands have a greater breaking strength than the transverse strands. Thus, when flexible grids such as these are used with a pin connection system the effect of the stress points is accentuated and failure can occur at an even earlier stage.
Yet another approach is to use intermediate connectors to connect a flexible grid to a block or blocks (see, for example, U.S. Pat. No. 6,019,550). Intermediate connectors usually take the form of a bar that connects to the grid, and which fits within a transverse recess in the upper surface of the block. Typically, the bar is provided with a plurality of projections that engage apertures in the flexible grid and which bear against the transverse edges of the apertures. Some disadvantages with this approach are that it requires additional parts, it requires machinery to fabricate the parts, it adds to construction time, and it requires user education and training. Moreover, the parts can be misplaced, misused, or damaged.
There is a need for a building block that may be used in conjunction with a flexible anchor grid. There is also a need for a building block that is able to directly engage a flexible anchor grid. There is yet another need for a building block that is able to position itself in an offset relation relative to building blocks in adjacent courses of blocks. And, there is a need for a simple and direct method of constructing a retaining wall in which building blocks used to construct the retaining wall can be connected to a flexible anchor grid.